The present invention relates to medical catheter design and use, and more particularly to the design of catheters utilizing laser-light energy for removal of blood vessel occlusions.
More than four million Americans suffer yearly from some form of arteriosclerotic coronary artery disease according to American Heart Association estimates. Arteriosclerosis, or obstruction of blood vessels with consequent interruption of blood flow, results from deposits of "plaque" within blood vessels' hollow lumina. Plaque consists of calcium, fibrous tissue, and fatty substances. It is categorized according to its calcium content. "Soft", recently-deposited, plaque contains small amounts of calcium, while "hard" or aged plaque contains proportionately greater amounts of calcium.
Efforts to find new procedures for improving blood flow through obstructed blood vessels have so far taken two directions. One technique is balloon angioplasty, also known as the "Gruntzig" balloon catheter technique. In this non-operative procedure, a "Gruntzig" catheter is delivered into an obstructed coronary artery. An inflatable balloon on the catheter tip is expanded at the site of obstruction or stenosis. Inflation of the balloon compresses plaque that forms the obstruction, widens the blood vessel lumen, and so improves blood flow. Balloon angioplasty works well on about 5% of all arteriosclerotic patients. The procedure works best when used to treat "soft" plaque obstructions in unconstricted arteries.
"Hard" plaque does not respond well to treatment by balloon angioplasty and necessitates more rigorous treatment procedures such as bypass surgery or endarterectomy. Surgical treatment for arteriosclerosis is associated with high morbidity and mortality rates, however, as well as tremendous costs and lengthy hospitalizations. Unfortunately, patients may suffer arterial spasms, embolization, thrombal occlusion and perforated blood vessels by use of this procedure.
A second approach to improving blood flow within obstructed vessels is that of laser vaporization. Continuous-wave laser energy delivered by flexible means to an obstructed site can effectively vaporize hard plaque and reopen a lumen to blood flow.
However, serious safety risks and laser-targeting problems accompany the use of laser vaporization in blood vessels. The amount of laser energy needed to vaporize hard plaque is also sufficient to vaporize healthy tissues. A primary difficulty, then, is the possible perforation of a vessel wall when a laser beam is targeted at an occlusion affixed to the wall. Especially risky and life-threatening is the treatment of coronary artery blockages by use of laser vaporization. In addition, since laser energy damages tissues by thermal necrosis or degradation, possible thermal damage may occur in tissues surrounding an occluded area.
Attempts to avoid such hazards and still allow use of the laser vaporization technique have resulted in a variety of designs for laser energy delivery systems. Flexible catheters having multiple internal channels emerged as a preferred means for this purpose. Channels within such catheters may carry an endoscope or guidewire, provide conduits for visualization media, gas injection, laser energy transmission, and/or suctionning tubes for debris removal. A catheter's degree of flexibility limits its usefulness for reaching obstructions within tortuously curved blood vessels and for permitting appropriate targeting of laser energy to effect vaporization.
In addition to multiple channels, a number of catheter designs disclose extensive use of inflatable balloons. Some balloons are placed external to the catheter and, when inflated, form a collar to secure the position of the catheter within a blood vessel and to prevent blood flow beyond the catheter. Other designs, as disclosed in U.S. Pat. No. 4,875,897 to Lee and U.S. Pat. No. 4,848,336 to Fox, include inflatable balloons within the catheter adjacent a distal end of the catheter that is positioned next to an obstruction in a vessel. Selective inflation of these internal balloons move optical fibers that transmit laser energy and permit appropriate targeting of the obstruction.
Control wires or cables provide an alternative method to internal positioning balloons for optical fiber movement. As shown in U.S. Pat. No. 4,913,142 to Kittrell et al., U.S. Pat. No. 4,669,467 to Willett et al., and U.S. Pat. No. 4,418,688 to Loeb, control wires may be affixed at or near a distal end of an optical fiber. Rotational or longitudinal movement of these wires permits a change in position of the distal end of an optical fiber to effect greater flexibility for targeting of the laser beam transmitted by the optical fiber. Applicant hereby incorporates by reference U.S. Pat. No. 4,669,467 to Willett et al.; U.S. Pat. No. 4,848,336 to Fox; and U.S. Pat. No. 4,913,142 to Kittrell et al.
Flexibility of the laser transmitting optical fiber within the catheter of known designs is severely restricted, however, due to inherent structural limitations. Catheter designs that lack internal positioning balloons or control wires have a targeting capacity limited to obstructions that lie in a straight path before them. Since blood vessels normally follow tightly curved paths, vessel wall perforation is a common problem. Catheter designs that include positioning balloons or control wires afford increased flexibility for targeting obstructions compared to less complicated catheter designs, but are still incapable of completely targeting obstructions located within tight vascular curves that approximate the distal end of the catheter as it is threaded through an obstructed blood vessel. Either catheter design requires an operator to frequently rotate or reposition a catheter within an obstructed blood vessel in order to cover a targeting range that meets or extends beyond a catheter's cross-sectional area. Repeated manipulation by an operator increases the level of operating difficulty and associated safety risks.
Structural limitations exist in presently known catheter designs that restrict handling and use of the catheter. For example, the presence of a number of internal balloons for aiming laser beams restricts the internal space available within a catheter required for related tasks and necessitates a multitude of connections for gas control, supply and escape routes. This, in turn, makes physical handling of the catheter cumbersome for an operator and limits the overall flexibility of the catheter. The same spatial and handling problems are encountered when numerous wires or cables are used for targeting laser beams.
Accordingly, it is the main object of the present invention to provide an improved laser delivery catheter which overcomes the deficiencies of the prior art.
It is another general object to provide an improved laser delivery catheter that consists of fewer components and so is less costly to manufacture.
It is a more specific object to provide a laser delivery catheter for transmission of laser energy that minimizes laser targeting requirements during operation.
It is yet another object to provide a simple laser delivery catheter with increased flexibility in order to reach occlusions located within sinuous blood vessels.
It is still another object to provide a laser delivery catheter that safely allows laser energy targeting beyond a cross-sectional area of the catheter.
It is yet another object to provide a laser delivery catheter with increased flexibility of the laser-delivery optical fiber within the catheter to permit targeting and vaporization of closely-occurring obstructions.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.